1. Field of the Invention
The present invention relates to a material for an electrode of a power storage device, a power storage device, and an electrical appliance.
2. Description of the Related Art
In recent years, a variety of power storage devices, for example, non-aqueous secondary batteries such as lithium ion batteries (LIBs), lithium ion capacitors (LICs), and air cells have been actively developed. In particular, demand for lithium ion batteries with high output and high energy density has rapidly grown with the development of the semiconductor industry, for example, portable information terminals such as mobile phones, smartphones, and laptop computers, portable music players, and digital cameras; medical equipment; and next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs). The lithium ion batteries are essential for today's information society as rechargeable energy supply sources.
A negative electrode of the power storage devices such as the lithium ion batteries and the lithium ion capacitors includes at least a negative electrode current collector and a negative electrode active material layer provided on a surface of the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material such as carbon or silicon, which can store and release lithium ions serving as carrier ions.
A negative electrode of a lithium ion battery using a graphite-based carbon material is formed by mixing graphite (black lead) that is a negative electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVDF) that is a resin as a binder to form slurry, applying the slurry over a negative electrode current collector, and drying the slurry, for example.
A lithium ion battery or a lithium ion capacitor has a problem in that irreversible capacity caused by repetitive insertion/extraction of lithium ions into/from the negative electrode active material is generated.
A negative electrode of a lithium ion battery or a lithium ion capacitor has an extremely low electrode potential and a high reducing ability. Accordingly, an electrolyte solution containing an organic solvent is reduced and decomposed, and decomposed matters form a film on a surface of the negative electrode. The formation of the film generates irreversible capacity, so that part of discharge capacity is lost.
As a technique for reducing the loss of discharge capacity, for example, a technique in which a surface of a negative electrode active material is covered with a metal oxide film, a silicon oxide film, or the like has been known (e.g., Patent Document 1). The formation of the above oxide film on the surface of the negative electrode active material can suppress formation of the film formed on the surface of the negative electrode due to the decomposition, and thus can reduce irreversible capacity.